1. Field of the Invention
The present invention relates generally to high temperature polymeric materials. It relates particularly to linear aromatic polyimides prepared by copolymerizing a bismaleimide with bis[4-(3,4-dimethylenepyrrolidyl)phenyl]methane.
2. Description of Related Art
A major goal in the field of high temperature polymers has been to prepare aromatic polyimides that can be easily fabricated with the required thermal and physical properties for aerospace applications. Recent research has been directed to achieve polyimides that are: (a) soluble in a common organic solvent; (b) melt-processable; and (c) thermally curable without the evolution of volatile by-products. See, for example: Mittal, K. L., "Polyimides: Synthesis, Characterization, and Applications", New York: Plenum Press, 1984; Cassidy, P. E., "Thermally Stable Polymers: Synthesis and Properties", New York: Marcel Dekker, Inc., 1980; and Hergenrother, P. and T. L. St. Clair, "Proceedings of Second International Conference on Polyimides", in Ellenville, New York, 1985.
The melt processability of polyimides can be enhanced by lowering the flow temperature, using synthetic techniques such as the incorporation of aryl-ether and meta-phenylene linkages in the polymer backbone.
A recent approach to obtain phenlylated polyimides involves the Diels-Alder polymerization of phenylated biscyclopentadienones with bismaleimides (see Harris, H., "Polyimides: Synthesis, Characterization and Application", ed., K. L. Mittal, p. 3., New York: Plenum Press, 1984). The problem with this process is that during the reaction, carbon monoxide is produced subsequent to the Diels-Alder addition. Furthermore, at temperatures greater than 300.degree. C., dehydrogenation, as well as other decomposition processes, occurs to yield a polymer with less solubility.